Visual–span profiles are plots of letter–recognitionaccuracy as a function of letter position left and right ofthe midline (Fig. 1). Previous research has shown that visual–spanprofiles are reduced in size in normal peripheral vision andthe reduction is correlated with reading speed (1). It is hypothesizedthat a reduced visual span is a primary factor limiting readingspeed in AMD patients with bilateral central scotomas. In thisstudy, we measured the visual–span profiles in AMD subjectsto test the prediction of an overall depression in visual–spanprofiles and to determine the effects of scotomas left or rightof the point of fixation.

Methods:

Eleven subjects with AMD and 3 age–matched normalswere tested. Visual–span profiles were measured usingthe trigram method described by Legge et al. (1). Letter sizewas approximately twice the subject’s critical print sizeand the exposure time for the letters was adjusted to achievea maximum accuracy of 80%. The size of the visual span was computedas the area under the curve in units of bits of informationtransmitted (Fig 1). The binocular visual field was mapped byTangent screen for AMD subjects to estimate the location andsize of scotomas.

Results:

The overall visual–span profiles for AMD subjectswere reduced in size when compared with normal controls. Areaof the visual–span profile, expressed as total informationtransmitted was significantly reduced in subjects with AMD (p<0.01).Eight of the 11 AMD subjects had central scotomas within thecentral 20°. These subjects exhibited localized depressionsin the visual–span profiles (Fig. 1), related to the locationof their scotomas. The size of the visual span was stronglycorrelated with the size of the binocular field loss in steradians(rs=–0.9, p<0.01).

Conclusions:

As predicted, visual–span profiles for peoplewith AMD were significantly reduced compared with normal controls.Localized depressions in the visual–span profiles wererelated to the location of scotomas measured with conventionalperimetry.